Casting tires

ABSTRACT

Casting tires having high strength and various excellent driving properties are produced by firstly casting (or molding) any one of a tread-crown portion on a case body portion with a high molecular weight substance and then prior to the completion of the curing of the firstly cast (or molded) substance, casting (or molding) the other portion with another high molecular weight substance having different physical properties from the former substance successively and curing both substances concurrently, said case body not containing any reinforcing material.

United States Patent Watanabe et al. Sept. 3, 1974 CASTING TIRES 2,902,072 9/1959 Reuter 152 330 3,208,500 9/1965 Knipp et al. [75] lnvemorsfi t hi z a fr 3,701,374 10 1972 McGillvary 152 357 A asu 11 a1 0; a0 a a em a; Hisa U t ll f T k Ja n ya m O 0 yo P? Primary ExaminerM. Henson Wood, Jr. Asslgneel Bl'ldgestone Tll'e Company Llmlted, Assistant Examiner-Robert Saifer Tokyo, Japan Attorney, Agent, or Firm-Fleit, Gipple & Jacobson [22] Filed: Sept. 28, 1972 [21] Appl. No.: 293,101 ACT Casting tires having high strength and various excel- [30] Foreign Applicatio P i it D t lent driving properties are produced by firstly casting Oct. 7 1971 Japan 46-78297 (or molding) any one of a tread'cmwn Pomon a case body portion with a high molecular weight sub- 52 US. Cl. 152/357 A 152/374 Stance and Prior to the COmph-ho of the curing 51 Int. c1. B600 5/00,160c 9/02 of the firshy Cast (of molded) Substance, casting (or [58] Field of Search 152/330, 354, 355, 357, mohhhg) the other "F ahmher molecu- 152/374 357 A, 361 R 357 R lar welght substance havmg d1fferent physlcal properties from the former substance successively and curlng [56] References Cited both substances concurrently, said case body not con- UNITED STATES PATENTS taining any reinforcing material. 2,224,141 12/1940 Clark 152/374 4 Claims, 16 Drawing Figures PATENTEU E FIG. 2A

8 7. 6 O O Q 70 80 90 Hardness (Sim/0A) FIG. 2B

60 70 Hardness (Shore A PATENTED 31975 p 2 0 0 0 0 Q t tk MBSE U PAIENTEDSEP 31814 I 3.833.043

sum 'our 15 force (K6) Max/mu Value of maring 40 50 so '70 I so. Tread Hardness (Shara/I PAIENIEDQEP 31914 agaasgms sum osor 1s FIG. 4 400L Cornering Force {K6 N 8 8 0-2" 4 6 f0 8/40 Angle 1 Pmmws I 7 3333.043

sum as or 15 Acce/ararion of Vibration (G) D D I Car Spud PATENTEBs'E'P 3:974

sum 01 ans;

FIG. 7

-0 3 w m \EE 9Q Begun axiom 0 I00 200 300 400 500 600 Modulus of Elasriciry Kg/cm PATENTED SH 3M4 sum -05 ur1s FIG. 9

A v m 8 6 4 2 w a.

0 4 w m m G3 8.8 u toso Slip Angle "I PAIENTED 3E? 31974 arm 10 ans FIG. /0

2 O. & Q E mo gtE muu Speed mmmscv m I $883,043

saw 11 or 15 III I FIG. 12

I ?\w i mass-n43 PAIENIEB'SIP 31914 FIG. 13

PAIENTED SHEEH1SUF15 CASTING TIRES The present invention relates to an improvement of pneumatic casting tires produced by casting-high molecular weight substances and to a process for producing improved casting tires.

The pneumatic tires can be considered to be a pressure tight container in which a pressurized gas in the inside of the tire is maintained under limited variation in dimension and further to be a structure which can endure various impact strength appliedfrom a road while rotating along the road.

It has been proposed to use reinforcing materials, such as fiber cords which have been used in the conventional tires produced by laminate molding, in the molding of casting tires from a high moleuclar weight substance but such a process reduces considerably such inherent merits of casting tires that the step for producing tires can be extremely simplified and further the drawback in tires resulting from the contained reinforcing material, such as cords, for example, the inner separation due to the use of such reinforcing materials, can be obviated. I

It has been attempted to produce casting tires of a unitary structure in which the tread-crown portion and the case body are formed by casting a common fluid high molecular weight substance and which have substantially the equivalent strength to the conventional tires containing reinforcing plies produced by laminate molding, although it has been able to satisfy the similar property as a durable pressure tight container to that of the conventional tires, the direction control of car (driving property of tires), the reducing of vibration from road (ride feeling) and the braking property (skid property) in wet road, which are another important properties in tires, have been very poor compared with those of the conventional tires and the practicable production has never commercially succeeded.

The inventors have made various investigations in order to obviate the drawbacks in the previous technics for producing the above described casting tires and accomplished the present invention. I

An object of the present invention is to provide casting tires which can attain the function as the durable pressure tight container basically required in the pneumatic tires and further are provided with the most important properties, which have been required in the presently improved motor car tires, that is, the excellent driving performance, ride feeling performance and skid performance.

The other object of the present invention is to pro vide pneumatic casting tires having excellent performance without reducing such inherent merits of the casting tires as the steps for producing tires can be extremely simplified and the drawbacks due to the housing of foreign reinforcing materials can be obviated.

It has been found that these objects can be attained by the following means.

1. Any reinforcing material, for example, fiber cords and other materials, is not used in the case body and the tread-crown (if necessary, bead wires are used as a member for reinforcing the bead portions).

2. The case body and the tread-crown of the tire form an integrated structure obtained by using fluid high molecular weight materials having different properties.

3. The case body is composed of a high molecular weight substance having a modulus of elasticity (in 50 percent elongation) of I40 Kg/cm 650 Kg/cm (approximately corresponding to Shore A hardness of 85 97) and the tread-crown is composed of a high molecular weight substance having Shore A hardness of 50 For a better understanding of the invention, reference is taken to the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of an embodiment of the casting tire according to the present invention;

FIGS. 2A and 2B are curves showing the relations between the coefficient of friction and the hardness of a tread material on a dry and a wet asphalt road, respectively;

FIG. 3 is a curve showing the relation between the cornering force and the hardness of a tread;

FIG. 4 is a curve showing the relation between the cornering force and the slip angle of various tires provided with treads having different hardness;

FIG. 5 is a partial cross-sectional view showing a modified embodiment of the present invention;

FIG. 6 shows the relation between the car speed and v the acceleration of vibration with respect to various tires;

FIG. 7 shows the relation between the modulus of elasticity and the spring constant of the case body;

FIG. 8 shows the relation between the car speed and the braking distance on a wet asphalt road;

FIG. 9 shows curves of the relation between the cor- .nering force and the slip angle;

FIG. 10 shows the relation between the car speed and the acceleration of vibration;

FIGS. 11 to 13 are cross-sectional views showing the steps for molding the tire according to the present invention; and

FIGS. 14A and 14B are cross-sectional view of the cores to be used in the casting process of the present invention.

Referring to FIG. I, 1 represents the casting tire according to the present invention which is an integrated structure consisting of a case body 3 provided with a pair of head wires 2 and 2 as circular reinforcing materials in both the bead portions and a tread-crown 4 forming the tire tread which surrounds the outer periphery of the crown of the case body 3.

As well known, the driving properties of tires are estimated by the cornering force which is a power acting between the tire tread and the road where the tire rotates and therefore relates to the coefficient of friction between the tire and the road.

Concerning to various materials for the tread to be used in tire I as shown in FIG. 1, the coefficient of friction between each of said materials and a dry asphalt road (FIG. 2A) or a wet asphalt road (FIG. 2B) was determined to obtain the results as shown in FIG. 2, in which the abscissa shows the Shore A hardness of the material and the ordinate shows the coefficient of friction. When the hardness becomes 75 the coefficient of friction in both the dry road and the wet road decreases rapidly and the driving performance and the braking performance are adversely affected.

The above described correlation between the coefficient of friction and the cornering force is more clearly shown particularly in the wet road. Namely, FIG. 3 shows the results obtained by determining the relation between the maximum values of cornering forces generated in tires rotating on a smooth road made of steel and the hardness of the treads in tires 1 made of various high molecular weight substances.

When the hardness of the material in the tread 4 becomes 75 85, the maximum value of the cornering force decreases rapidly and such phenomenon shows a very dangerous status for the car running in the rain.

This relation appears in a dry road in a more complicated state, because the cornering force which arises between the road and the surface of tread is transmitted to the wheel and car successively through the case body 3 but when the tread crown 4 is too soft (the hardness is low), the resilient force against a given displacement is small and the gain of the cornering force within the practical range of the slip angle (angle between the direction of the rotating face of tire and the advancing direction) rather decreases.

This phenomenon will be explained with reference to FIG. 4, which shows the results obtained by determining the cornering force against the slip angle when the materials to form the tread-crown 4 in the pneumatic tire as shown in FIG. 1 are changed variously and the curves A, B, and C show the characteristics obtained in the tires provided with the treads made of the materials having the hardness of 85, 63, and 48, respectively.

The curve A shows the typical state where the hardness is too high and at the slip angle of about 6 thecornering force reaches the maximum value and then decreases rapidly and such tires are very dangerous for the car-driving.

The curve B shows the state where the hardness of the tread is moderate and the cornering force increases steadily within the practical range of the slip angle l0) and such tires are consequently superior in view of controlling of the driving of motor car properly.

The curve C shows the state when the hardness is further low and the relation between the slip angle and the cornering force is similar to the curve B but the absolute value is lower and such tires are not desirable in view of the control of driving of car.

An explanation will be made with respect to the case body 3.

Since the case body 3 of the tire I is formed of an isotropic high molecular weight substance having no reinforcing cord layer, the material for the case body must have such a strong physical property that the tire is not easily expanded by the pressure of air filled in the interior of the tire. For this purpose, the modulus of elasticity of the material for the case body 3 must be at least 140 Kg/cm'-.

Another important role of the case body 3 in view of the safety is to endure any impact strength applied to the tire from outside during running in addition to the resistance against the pressure of air in the interior of the tire.

It has been previously taught experimentally that the tensile strength to be provided in the materials for the case body is to be more than eight times of the maximum stress which is generated in this portion only by the charge of air. ln the tires of the conventional passenger car, the maximum stress due to the pressure of the charged air is less than Kg/cm and therefore the tensile strength which is required for the materials for the case body is more than 160 Kg/cm When this value is converted to the hardness, said value corresponds to about 85 and consequently if the treadcrown 4 is formed of such a material, the driving performance is not satisfied as mentioned above and therefore it is impossible to manufacture the tire with a unitary material and an improved tire structure according to the present invention is demanded.

Another important performance for the tire is the ride feeling and in the tires of the present invention in which the tread-crown and the case body have different physical properties, the impact from the road is absorbed by the soft tread-crown and therefore such tires are advantageous also in this point.

The acceleration of vibration subjected to each of the cars provided with conventional casting tires (B) in which the tread-crown and the case body are formed of a common material, novel tires (A) according to the present invention in which the tread-crown and the case body have different physical properties and conventional tires (C) provided with reinforcing cord layers, respectively, are run on a considerably uneven road, was determined to obtain the results as shown in FIG. 6, which shows that the ride feeling of the casting tire (A) according to the present invention is far superior to the tire (B).

As mentioned above, the tires must satisfy the performance required as a pressure tight container but if this requirement is estimated too high and a material having an extremely high modulus of elasticity is used for the case body, the vertical spring constant of the whole tire, which is recognized broadly as a property having a close relation to the ride feeling, exceeds the upper limit of 30 Kg/mm (preferably 27 Kg/mm) toler ated in the pneumatic tires and therefore such a material is not preferable.

FIG. 7 shows the results obtained by determining the relation of the modulus of elasticity to the vertical spring constant of the case body with respect to the tire size 6.95 l4 and in order to suppress the vertical spring constant to less than 30 Kg/mm, the upper limit of modulus of elasticity of the material for the case body must be 650 Kg/cm Furthermore, the case body is repeatedly strained while the tire is running and the fatigue in the case body increases with the increase of running distance.

On the other hand, it is essentially impossible to prevent the rapid decrease of fatigue resistance for bending of the material with increase of the modulus of elasticity. so that it is impossible to use the material having an extremely high modulus of elasticity.

The tread-crown 4 of the tire is subjected to deformation repeatedly by rolling and consequently the energy loss in the interior of the material appears as heat and therefore the hardness decreases. The hardness must be larger than the above described lower limit under even in running condition.

The tread-crown 4 must be provided with the pattern grooves 5 in order to secure the tire performance but in the bottom of the grooves the stress concentration occurs owing to the deformation of tire and therefore a relatively soft material having a high bending fatigue resistance-is selected as mentioned above and further it has been found that by making the thickness from the bottom of grooves to the boundary AA between the tread-crown 4 and the case body 3 as large as possible and more than 10 percent of the depth of the grooves, the generation of cracks in the bottom of grooves due to the stress concentration can be prevented and even if the cracks are formed, the hard case body 3 is not substantially damaged by the formed cracks.

From the results of the experiment, the thickness of less than percent is liable to cause a large amount of cracks in the bottom of the tread grooves, while if the thickness is too large, the shape balance as a superior tire can not be maintained and therefore the upper limit must be about 40 percent.

It is effective for preventing the inter-layer separation of the ends of the boundary AA between the treadcrown 4 and the case body 3 to form said ends in buttress as shown in FIG. 1 but as the case may be, the boundary AA are terminated at the shoulder S as shown in FIG. 5 and in this case the shoulder S is formed of the material forming the case body 3.

The effectiveness of the invention will be explained with reference to the following example.

FIG. 8 shows a relation between the braking distance and the running speed when water is sprayed on a particularly slidable asphalt road, FIG. 9 shows a relation between the cornering force and the slip angle of various tires measured by means of a driving tester provided with a wooden surface and FIG. 10 shows a relation between the acceleration of vibration and the running speed of the car running on a considerably uneven road.

The tires to be tested are as follows and the size in each of them is 6.94 14 for passenger car and the dimension is within the JIS specification.

A is the tire of the present invention in which the tread-crown and the case body are composed of different high molecular weight substances and the case body is formed of a material consisting essentially of ether type polyurethane and having a modulus of elasticity of 300 Kg/cm (Shore A hardness of 88) and the thickness in the center of the tread-crown and the sidewall are 12.5 and 6 mm, respectively. On the other hand, the tread-crown is formed of a material consisting essentially of a synthetic rubber (SBR) or natural rubber and having a modulus of elasticity of 60 Kg/cm (Shore A hardness of 67) and the thickness of the center is 10 mm.

B is a conventional casting tire in which the treadcrown and the case body are formed of a common high molecular weight substance consisting essentially of ether type polyurethane having a modulus of elasticity of 220 Kg/cm (Shore A hardness of 84) and the thickness in the center of the tread-crown and the sidewall are 19.5 and 6 mm, respectively.

C is a conventional bias tire consisting of the carcass formed of 2 plies of polyester cords of 1,260 denier/2 and atread-crown consisting essentially of a synthetic rubber (SBR) or natural rubber having a modulus of elasticity of 35 Kg/cm (Shore A hardness of 55), in which an angle between the carcass cord and the circumferential direction in the tread-crown is 35.

D is a radial tire provided with a non-stretchable belt in the circumferential direction of the tread in which the carcass is composed of two plies of rayon cords of 1,650 denier/2 and the breaker has four belts corn-' posed of non-stretchable rayon cords of 2,200 denier/2, the angle between the cord and the circumferential direction of the tire being at the center of the tread-crown and the tread-crown is formed of rubber consisting essentially of synthetic rubber (SBR) or nat ural rubber and having a modulus of elasticity of 42 Kg/cm (Shore A hardness of 62).

FIG. 8 shows the performance of tires in the rain,

which has become important because of the recent demand of increase in speed. The tire A of the present invention in which the tread-crown and the case body have different physical properties has a highly improved skid characteristic as compared with the conventional casting tire B which is very poor in the braking property on the wet road.

The advantage obtained by using a softer material for the tread-crown than the material for the case body consequently appears in the ride feeling and FIG. 10 shows that the ride feeling of the tires A of the present invention'is near that of the bias tires C.

If other performances (particularly the driving performance) are decreased by the improvement of the performance in the rain and the ride feeling, the effect of such improvement has no significance. However, from the results of the test for the driving performance in FIG. 9, it can be seen that there is no'such a fear.

Then an explanation will be made with respect to the process for producing the casting tires of the present invention.

In the tires according to the present invention in which the tread-crown 4 and the case body 3 are integrated by different materials, there is a problem in the inter-layer adhesivity between the case body 3 and the tread-crown 4.

For example, it can be considered that the case body 3 and the tread-crown 4 are cast and cured in separate molds and then an adhesive is applied on the boundary surface to be bonded and then both molded bodies are integrated mechanically but in such a manner the durability of the adhered layer will not be ensured under the severe conditions when using the tires.

Thus, in the present invention a common mold is used for casting the case body 3 and the tread-crown 4 and casting is effected successively in order to make the chemical bond strong in the boundary between the tread-crown and the case body.

Namely, the material for the tread-crown is cast (or molded) in a mold for forming the tread-crown and then when the curing reaction is proceeding, the said mold is combined with a mold for forming the case body 3 in the state where the tread-crown is held in the tread-crown forming mold and the material for the case body is cast thereinto and the curing reaction of the tread-crown and the case body is continued concurrently.

Alternatively, in the reverse order, the casting of the case body 3 is preceded and the mold holding the case body is combined with the mold for forming the treadcrown and successively the tread-crown 4 is cast (or molded) and the curing reaction is continued together with the case body 3. In this case the core 7 in FIG. 11 is not necessary, but instead of this core 7, an outer mold (not shown in the drawing) for forming the boundary AA in FIG. 1 must be set prior to the molding of the tread-crown.

By such a successive casting process, the chemical bond between the tread-crown and the case body is not only strengthened but also any error in the formation of the adhering face is observed in the mechanical assembling of the tread-crown and the case body is not made.

As an embodiment, FIG. 11 shows the step for casting the tread-crown 4. By two tread forming molds 6, 6 which can be separated on an equator of a tire to be produced and a core 7, a cavity is formed and a high molecular weight substance suitable for forming the tread-crown is cast into said cavity.

In this case, the tread forming molds 6 and 6', the core 7, the bead portion forming two splitting molds 8 and 8 which are closely fitted at the center thereof by a projection-groove joint and the sidewall forming molds 9 and 9' are arranged as shown in FIG. 11.

The curing reaction in the tread-crown 4 starts successively after the completion of casting the material for the tread-crown into the above described cavity and in the course of the reaction, particularly in the semicured state, casting of the case body is started without removing the tread forming molds 6 and 6'. Namely, the sidewall forming molds 9 and 9 and the bead forming molds 8 and 8 are opened as shown in FIG. 12 and the core 7 is taken out and replaced with a core which coincides with the shape of the inner periphery of the case body 3 and the bead portion forming molds 8 and 8' and the sidewall forming molds 9 and 9 are again set as shown in FIG. 13.

Taking out and setting of the cores 7 and 10 can be easily effected by such a structure that the jointing faces 11, ll, 12, and 12' of the sidewall, forming molds 9 and 9' to the tread forming molds 6 and 6 and the bead portion forming molds 8 and 8 form conical faces which reach the terminals of the crown portion and the head portion.

lnto the cavity formed between the already cast tread-crown portion 4 and the molds 8, 8', 9, and 9 and the core 10, in the bead portion in said cavity bead wires 2 and 2 having been already set, a high molecular weight substance suitable for the case body 3 is cast.

FIG. 13 shows the cross-section of the tire mold assembly where the case body 3 has been cast so as to form a unitary structure together with the tread-crown 4. The case body 3 is molded into a given form in the cavity surrounded by the tread-crown 4, the core 10, the bead portion forming molds 8 and 8 and the sidewall forming molds 9 and 9'.

Each of the cores 7 and 10 to be used in the above described process is preferably formed into a given shape by injecting a gas into a unitary structure constituted with a high molecular weight substance and these cores may be provided with fiber cord or canvas reinforcing layer 13 as shown in FIG. l4-A or may be provided with a pair of beads 14 and a fiber reinforcing layer 13' fixed to the beads as shown in FIG. 14-B.

Alternatively. the tread-crown 4 may be formed by shaping a usual tread extruding rubber or a rod shaped unvulcanized rubber by means of tread forming molds 6 and 6.

In this case, the vulcanization of this rubber needs a temperature of 160C and if polyurethane is used as the case body 3 to be integrated with this rubber, the polyurethane should not be heated to a temperature higher than C and therefore it is preferred that the treadcrown 4 is previously shaped and after the vulcanization of said tread-crown has advanced, the casting of the case body 3 is effected.

Thus, according to the present invention, the strength and performance necessary for a container for keeping the inner pressure of the pneumatic tires can be satisfied by the case body 3 and the ride feeling, skid resistance, durability and the like of the pneumatic tires can be satisfied by the tread-crown 4, accordingly the casting tires of the present invention can provide all performances required for the practical tires and since the case body does not need any reinforcing means, such as cords, except for the bead, the casting tires of the present invention can satisfy the simplification of the production steps which is the characteristic for the casting tires and further obviate any trouble resulting from the embedding of the reinforcing material and the tread-crown and the case body can be tightly and strongly integrated by the chemical bond.

What is claimed is:

l. A pneumatic casting tire consisting of a treadcrown having patterned grooves in the road-engaging surface thereof and a case body integral with said tread-crown, said case body being of doughnut-like shape with a hollow interior and an open inner periphery, said case body having side walls extending from said tread-crown and terminating at a pair of spaced bead portions, said case body being composed of high molecular weight polymeric substance having a modulus of elasticity at 50 percent elongation of to 650 Kg/cm and containing no reinforcing material, the thickness from the bottom of said grooves to the boundary between said tread-crown and said case body being 10 to 40 percent of the depth of said grooves, and said tread-crown being composed of a high molecular weight polymeric substance having a Shore A hardness of 50 to 75.

2. Casting tires as claimed in claim 1, wherein both sides of the tread are formed with the same material as the case body.

3. Casting tires as claimed in claim 2, wherein said case body is composed of ether type polyurethane and said thread-crown is composed of styrene-butadiene rubber or natural rubber.

4. Casting tires as claimed in claim 1, wherein said case body is composed of ether type polyurethane and said tread-crown is composed of styrene-butadiene rubber or natural rubber. 

1. A pneumatic casting tire consisting of a tread-crown having patterned grooves in the road-engaging surface thereof and a case body integral with said tread-crown, said case body being of doughnut-like shape with a hollow interior and an open inner periphery, said case body having side walls extending from said tread-crown and terminating at a pair of spaced bead portions, said case body being composed of high molecular weight polymeric substance having a modulus of elasticity at 50 percent elongation of 140 to 650 Kg/cm2 and containing no reinforcing material, the thickness from the bottom of said grooves to the boundary between said tread-crown and said case body being 10 to 40 percent of the depth of said grooves, and said tread-crown being composed of a high molecular weight polymeric substance having a Shore A hardness of 50* to 75*.
 2. Casting tires as claimed in claim 1, wherein both sides of the tread are formed with the same material as the case body.
 3. Casting tires as claimed in claim 2, wherein said case body is composed of ether type polyurethane and said thread-crown is composed of styrene-butadiene rubber or natural rubber.
 4. Casting tires as claimed in claim 1, wherein said case body is composed of ether type polyurethane and said tread-crown is composed of styrene-butadiene rubber or natural rubber. 